THE sister of Femi Nandap who stabbed popular lecturer Jeroen Ensink to death told police she had concerns for his mental health six months before the killing, an inquest heard.

Nandap is serving a indefinite hospital order for stabbing 41-year-old Dr Ensink in a random attack in December 2015.

He had been arrested in May 2015 for allegedly assaulting a police officer and being in possession of a knife in Belsize Park.

The charges were dropped by the Crown Prosecution Service six days before his violent attack on Dr Ensink, a senior lecturer at London School of Hygiene and Tropical Medicine who had left his Hilldrop Crescent home to post cards announcing the birth of his first child Fleur.

His widow Nadja Ensink-Teich wants the inquest at St Pancras Coroner’s Court to answer how Nandap, a then 23-year-old suffering from paranoid schizophrenia, was at liberty on the day he killed her husband.

Wupya Nandap told jurors on Tuesday she had told police not to interview her brother in May without an “appropriate adult” expressing concerns for his mental health.

Dr Ensink with his wife Nadja

Ms Nandap, a corporate lawyer, said: “I think at the moment I knew he was being held I think I would have said ‘I do not think he is mentally well’.”

However, she claims police said he had been assessed by a doctor who said Nandap was fit to be interviewed in custody.

When asked by Bo-Eun Jung, representing the Met, whether it could be the case she was asked to be the appropriate adult, Ms Nandap responded: “I do not think it did happen as if I was asked to be an appropriate adult I would gone down there.”

The inquest previously heard two police officers admitted they had not submitted “Merlin” reports – which would have flagged up concerns about Nandap’s mental health. Both said in “hindsight” they would have.

Ms Nandap said she had some concerns about her brother’s mental wellbeing since the beginning on 2015, when he had become “withdrawn” and had became obsessed with conspiracy theories including on giants, aliens and the Bible.

She said he was smoking cannabis which “exacerbated” his condition.

Ms Nandap had previously suggested he see a doctor or professional. The night after he was arrested, and subsequently bailed, he boarded a flight home to Nigeria for mental health treatment and to be close to his family, she told the inquest.

While there, Ms Nandap, who lives in London, was told by her family he saw a doctor and psychiatrist and also saw some local healers.

A doctor provided a letter to Ms Nandap to say he was not able to attend a court hearing in August because he was “not fit to travel”, which she gave to police.

Nandap returned to the UK in October where he was arrested at Heathrow airport. Ms Nandap said although she spoke to the police about her brother, she did not again raise concerns about his mental health.

On his return to the country, Ms Nandap said he was on medication after being diagnosed with psychosis and acute depression. She added: “He seemed a lot better, he had less of a vacant expression on his face, his personal hygiene seemed better.”

She said their relationship was “fragile” adding: “He seemed to shut down when I brought up this issue [of mental health] so I did not want him to draw away more than he already had. I just used my judgement to when I thought I would ask him.”